The present invention relates to a process and to an apparatus for continuous living polymerization of cationically polymerizable monomers, in which at least three feedstocks are mixed in one or more mixers with microstructures and then polymerized in at least one reaction zone.
The preparation of polymers and especially of polyisobutenes by living cationic polymerization of the parent monomers is known. Living cationic polymerization refers generally to the polymerization of cationically polymerizable monomers and especially of isoolefins or vinylaromatics in the presence of metal halides or semimetal halides as Lewis acid catalysts and tert-alkyl halides, or benzyl or alyll halides, esters or ethers as initiators, which form a carbocation or cationic complex with the Lewis acid. A comprehensive review of this subject can be found in Kennedy/Ivan, “Carbocationic Macromolecular Engineering”, Hauser Publishers 1992.
The advantage of living cationic polymerization is that polymers with relatively narrow molecular weight distributions are obtained. However, a narrow molecular weight distribution is obtained only when the polymerization is carried out at very low temperatures which generally must not be above −70° C. Processes which have to be carried out at such low temperatures are, however, often scarcely implementable and uneconomic on the industrial scale. Continuous processes for living cationic polymerization usable on the industrial scale are to date unknown.
WO 99/54362 describes a process for continuous free-radical solution polymerization, in which at least two reactants are conducted through a micromixer and combined, mixed with one another and then polymerized in a tubular reactor.
It was an object of the present invention to provide a more economically viable process for living cationic polymerization. More particularly, the process should be performable continuously and should allow performance at higher temperatures than the prior art processes, without leading to molecular weight broadening of the products obtained thereby.